The parliamentary rites of passage began officially for S.790 yesterday, and for supporters of the bill almost everything came up roses.

In a hearing before a Senate Public Works subcommittee considering the legislation, which would require barges to pay tolls to use the nation's inland waterways, S. 790 found three partial friends and one enemy among senators, and an all-out advocate from the academic world.

The academician, a white-haired, tweed-suited gentleman who could paly an Ivy League economics professor in the movies if he were not one in real life, was Dr. William Vickery, an expert on transportation economics from Columbia University.

Reading from a richly polysyllabic statement in his deep, rumbling voice, Vickrey said a system of waterway fees would benefit consumers, the government and even the barge operators who would have to pay the tolls.

Since the government first began building waterways immediately after the revolution, barge traffic has moved free of tolls or taxes. Barge operators say instituting tolls now would increase the costs of goods moved by water -- mainly food, fuels and steel -- and would cause serious economic dislocation in the water freight industry.

Vickrey took issue with both points.

He said waterway tolls would eliminate an "artificial" rate advantage enjoyed by water shippers, leading to "efficient allocation of [freight] traffic among [transportation] modes." With each shipment moving by the most efficient means, he said, the nation's total transportation bill would be reduced.

On the waterways, tolls would eliminate congestion, Vickrey said, reducing the time needed for each shipment and thus reducing barge operators' net costs.

The professor's arguments were cloaked in academic jargon -- he made much of "distributional impacts" and "the intra-marginal residue of costs" --mittee members, but Sen. Pete V. Domenici (R-N.M.), sponsor of the waterway toll bill was nonetheless clearly delighted.

"I gather you're telling us that user charges. . . will have a net effect that benefits the consumer," Domenici said, and he beamed when Vickrey agreed. Before Vickrey left the hearing, Domenici took pains to establish that the professor had not been paid for his testimony by the railroads or competitors of barge operators.

Yesterday's hearing, which was arranged after considerable parliamentary maneuvering on Domenici's part, also dealt with a proposal to build a new $400 million lock and dam on the Mississippi River at Alton, Ill.

Sens. Adlai E. Stevenson (D-Ill.), Charles H. Percy (R-Ill.) and John Danforth (R-Mo.) advocated immediate construction of the facility, saying it is essential for unimpeded barge traffic on the nation's main water freight route.

Percy also endorsed the waterway toll legislation, which he said would end a "grossly unfair" subsidy that penalizes competing modes of shipment.

Stevenson and Danforth said they agreed with the "principle" of waterway charges, but both suggested that more study might be required before tolls could be instituted. They both expressed concern that Domenici's controversial toll plan would kill the new lock and dam if the two issues come to the Senate floor together.

Sen. Dewey F. Bartlett (R-Okla.) was the only senatorial witness who came right out and said he was opposed to the waterways tolls.

He was concerned, he said, that a toll system would reduce traffic on the new Arkansas River Navigation System, a $1.2 billion waterway that has made Tulsa, Okla., a seaport.

Conspicuously absent from yesterday's session were representatives of the executive agencies that build the waterways and determine national transportation policy.

They had turned down invitations to the hearing, saying the Carter administration needed more time to settle on a position on the issue.